The present invention relates to compacts made from pyrogenically produced oxides, the method of their production and to the use of such compacts as catalyst supports or as catalysts.
The production of compacts or pressed parts from pyrogenically produced silicon dioxide is known in the art. For example, In U.S. Pat. No. 5,086,031 compacts are described having an outside diameter of 2 to 15 mm and a fracture breaking strength of 50 to 150 N. They can be used as catalysts in the hydration of ethylene to ethanol as well as other reactions. U.S. Pat. No. 5,086,031 assigned to the same assignee as this invention is relied on and incorporated herein by reference.
However, the known compacts have the disadvantage that when they are used e.g. as catalysts in the hydration of ethylene in fixed-bed reactors, additional support-, covering- or facing layers, e.g. of coal, metals such as copper, ceramic materials or mineral materials such as mullite must be used (cf. Marshall Sittig, Handbook of Catalyst Manufacture, Noyes Data Corporation, USA, 1978).
As a result of the different chemical composition of the support-, covering- or facing layers, impurities, which can possibly result in undesired side reactions, are carried into the reaction mixture.
There was thus a need to find a material for the support-, covering- or facing layers which does not carry any impurities into the reaction mixture.